1. Field of the Invention
This invention relates to medical components, such as a syringes, tubes or medical collection devices, having coated surfaces which can exhibit good frictional properties and provide a neutral surface that does not adversely affect biological materials and pharmaceutical materials in contact therewith.
2. Description of Related Technology
Traditionally, containers for chemically sensitive materials have been made from inorganic materials such as glass. Glass containers offer the advantage that they are substantially impenetrable by atmospheric gases and thus provide a product with a long shelf life. However, glass containers can be fragile and expensive to manufacture.
More recently, lighter and less expensive containers made of polymeric materials are being used in applications in which traditional glass containers were used. These polymeric containers are less susceptible to breakage, lighter, and less expensive to ship than glass containers. However, polymeric containers can be permeable to gases, permitting atmospheric gases to pass through the polymeric container to the packaged product and also permitting gases in the packaged product to escape through the polymeric container, both of which undesirably degrade the quality and shelf life of the packaged product.
Whether the container is formed from glass or polymeric material, reactivity of the interior surface of the container with the contents of the container, such as biological materials and/or drugs, can be problematic. Trace components of the glass or polymeric material and coatings on the interior of the container may migrate into the container contents, and/or components of the container contents may migrate or react with the interior surface of the container.
Also, certain devices, such as syringe barrels, require slow and controlled initiation and maintenance of sliding movement of one surface over another surface. It is well known that two stationary surfaces having a sliding relationship often exhibit sufficient resistance to initiation of movement that gradually increased force applied to one of the surfaces does not cause movement until a threshold force is reached, at which point a sudden sliding or shearing separation of the surfaces takes place. This sudden separation of stationary surfaces into a sliding relationship is herein referred to as “breakout” or “breakloose”.
“Breakout force” refers to the force required to overcome static friction between surfaces of a syringe assembly that has been previously moved in a sliding relationship, but has been stationary (“parked” or not moved) for a short period of time (for example, milliseconds to hours). A less well known but important frictional force is “breakloose force”, which refers to the force required to overcome static friction between surfaces of a syringe assembly that have not been previously moved in a sliding relationship or have been stationary for longer periods of time, often with chemical or material bonding or deformation of the surfaces due to age, sterilization, temperature cycling, or other processing.
Breakout and breakloose forces are particularly troublesome in liquid dispensing devices, such as syringes, used to deliver small, accurately measured quantities of a liquid by smooth incremental line to line advancement of one surface over a second surface. The problem also is encountered in devices using stopcocks, such as burets, pipets, addition funnels, and the like where careful dropwise control of flow is desired.
The problems of excessive breakout and breakloose forces are related to friction. Friction is generally defined as the resisting force that arises when a surface of one substance slides, or tends to slide, over an adjoining surface of itself or another substance. Between surfaces of solids in contact, there may be two kinds of friction: (1) the resistance opposing the force required to start to move one surface over another, conventionally known as static friction, and (2) the resistance opposing the force required to move one surface over another at a variable, fixed, or predetermined speed, conventionally known as kinetic friction.
The force required to overcome static friction and induce breakout or breakloose is referred to as the “breakout force” or “breakloose force”, respectively, and the force required to maintain steady slide of one surface over another after breakout or breakloose is referred to as the “sustaining force”. Three main factors, sticktion, inertia, and dimensional interference (including morphology) between the two surfaces contribute to static friction and thus to the breakout or breakloose force. The term “stick” or “sticktion” as used herein denotes the tendency of two surfaces in stationary contact to develop a degree of adherence to each other. The term “inertia” is conventionally defined as the indisposition to motion which must be overcome to set a mass in motion. In the context of the present invention, inertia is understood to denote that component of the breakout or breakloose force which does not involve adherence.
Breakout or breakloose forces, in particular the degree of sticktion, vary according to the composition and dimensional interference (related to morphology) of the surfaces. In general, materials having elasticity show greater sticktion than non-elastic materials. The length of time that surfaces have been in stationary contact with each other also influences breakout and/or breakloose forces. In the syringe art, the term “parking” denotes storage time, shelf time, or the interval between filling and discharge. Parking time generally increases breakout or breakloose force, particularly if the syringe has been refrigerated or heated during parking.
A conventional approach to overcoming breakout or breakloose has been application of a lubricant to a surface interface. Common lubricants used are silicone or hydrocarbon oils, such as mineral oils, peanut oil, vegetable oils, and the like. Such products have the disadvantage of being soluble in a variety of fluids, such as vehicles commonly used to dispense medicaments. In addition, hydrocarbon oil lubricants are subject to air oxidation resulting in viscosity changes and objectionable color development. Further, they are particularly likely to migrate from the surface to surface interface. Such lubricant migration is generally thought to be responsible for the increase in breakout or breakloose force with time in parking. As a separate issue, the lubricant can also migrate into the contained solution causing undesirable interactions with or instability of the active biological materials, drugs, pharmaceutical ingredients or excipients. This contact may occur on the surface of the silicone coated container or on the silicone droplet that has been sloughed into the bulk of the liquid contained in the syringe.
Thus, there is a need for a lubricity mechanism to overcome high breakout and breakloose forces whereby smooth transition of two surfaces from stationary contact into sliding contact can be achieved. Also, there is a need for an improved barrier coating to prevent leaching of materials from a container or seal surface into the container contents and/or from the container contents into the container or seal surface, and to prevent gas and/or water permeability in medical articles, such as syringes, tubes and medical collection devices.